Conventionally, fluid filled bedding includes air filled bedding (e.g. air mattresses, air pillows) and fluid filled bedding (e.g. waterbed and water pillows), are available.
A conventional air mattress and air pillow support a human body mainly with tension of an air-sealed bag (bag body). However, pressure generated by the tension of a bag body and supports the human body, is extremely uneven in different regions, depending on the shape of the part of the human body the bag is supporting. The pressure also widely varies depending on the state of contact between the bag body and the human body. Accordingly, the bedding fails to consistently support the human body with uniform pressure, resulting in uncomfortable sleep.
In the conventional waterbed and water pillow with no frame, in order to maintain the shape of the bedding, an approximately equivalent amount of water corresponding to the maximum volume of the inner space of the water-sealed bag body has to be filled therein. Since a large ratio of the force supporting the human body is tension working on the bag, comfortable sleep is not obtained.
One prior art solution is a technique to maintain the shape of the bedding while reducing the volume of the fluid-sealed bag body therein. Specifically, a bedding having an elastic body with continuous air bubbles formed into a desired shape is inserted in the bag body. The surface of the elastic body and the inner surface of the bag body are all bonded to each other so as to maintain the shape as bedding. However, since the bag body is bonded to the elastic body via the surfaces thereof, there is not enough flexibility to deform freely. Therefore, when the human body is supported, a high ratio of the tension of the bag body in the force of supporting the human body is created.
Another current solution to reduce the ratio of the tension in the force supporting the human body is by creating a looseness in the water-sealed bag at where the bag comes into contact with the human body. To maintain the configuration as bedding, a part of the bag is formed of a solid material, or the periphery of the bag is enclosed with a solid material. Though almost all force of the human body is born by buoyancy, this technique is only practical in a large bed where the solid portion does not come into contact with the human body. Furthermore, to obtain enough buoyancy, liquid of considerable depth has to be sealed inside the bed. Accordingly, the bed is very heavy, making it difficult to install.
As described above, no conventional bedding comfortably supports a head or an entire body by means of buoyancy at a constant pressure, nor being light in weight, small in size, and inexpensive in cost.